20.7.14 Accessing Scroll Bar Events

These functions are useful for decoding scroll bar events.

— Function: scroll-bar-event-ratio event

This function returns the fractional vertical position of a scroll bar
event within the scroll bar. The value is a cons cell
(portion . whole) containing two integers whose ratio
is the fractional position.

— Function: scroll-bar-scale ratio total

This function multiplies (in effect) ratio by total,
rounding the result to an integer. The argument ratio is not a
number, but rather a pair (num . denom)—typically a
value returned by scroll-bar-event-ratio.

This function is handy for scaling a position on a scroll bar into a
buffer position. Here's how to do that: